Capacitors, which can be rapidly charged and discharged, have been developed as a standby power supply used when an abnormal state occurs in a main power supply of an electronic apparatus. Among these capacitors, electric double layer capacitors have been drawing particular attention because of their large capacitance. Positive and negative electrodes of an electric double layer capacitor contain activated carbon having a very large surface area to adsorb ions.
To improve characteristics of electric double layer capacitors, such as durability and temperature characteristics, it has been proposed that the ratio of the volume of the electrolytic solution with respect to the volume of the voids in the polarizable electrodes and in the separator be controlled in an appropriate range (for example, Patent Literature 1).
The currently available electric double layer capacitors, however, severely degrade their characteristics when repeatedly charged and discharged.